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A cautionary tale about overnight battery charging

02-25-2019, 06:43 PM

So the other day I had a narrowly avoided close call that could have been catastrophic. Hopefully you all can learn from my mistake...

A couple of months back I hastily inserted my key to lock my shark pack onto my bike into the charging port instead of the lock as the bike was turned the opposite way from its normal position after working on it the night before. It caused an immediate short with the expected violent sparking, but fortunately I pulled the key back quickly and the battery was still functional with the port and the key only a little damaged. I went to charge it that night and the connection worked, but was a little loose and janky. I knew that it was something that I should address and fix, but life got busy and it was working well enough as is so I left as it was with plans to get to it at a later date.

I've always suspected that the fears about batteries catching fire while charging were overblown and after many, many charges without incident decided to start charging mine inside the house as it's winter and charging mine outdoors in the cold would potentially shorten its life. As fate would have it, the problem happened the first time that I forgot to charge it during the evening when I got home and decided to do it overnight, and I only narrowly avoided burning my house down.

I got up that morning to find the plug into connector pretty much welded to the battery. It had shorted at some point during the night, and luckily, as the plastic melted it caused a barrier that stopped the short before things got really ugly. I was able to swap it out for an XT60 which works fabulously so all is well with the battery now, but it really highlighted the danger of charging a battery with a janky connection. Connectors are often a point of weakness and danger in an electrical system and it was a total bonehead move of mine to charge my battery in the house, overnight, with a known connector problem. So don't be a dumbass like me. If your connection is a little messed up, fix it before it causes a problem. The swap out for the XT60 was easy and way more secure. I'm frankly surprised that batteries don't come with this connection by default - it really is that much better. I'd be especially concerned if I had one of the older Luna shark packs like mine as that connection is a known problem area (per the reviews on lunacycle.com) Their shark pack was recently redesigned and hopefully the new one has remedied this problem. In any case I wanted to share my story so that you call can all be aware of the danger and learn from my mistake.

Comment

That kind of accidental key shorting is the exact reason the pack was switched to mini-xlr. We take a decent amount of flak when we have to break backwards compatibility like that but when it comes to safety upgrades it is almost always going to be worth it. Glad you are safe, that could have ended a lot differently.

Comment

I always charge in an ammo case because as soon as they start burning, they are VERY difficult to extinguish. This makes me feel very comfortable charging overnight, although in the garage, not the house.

Comment

Charge time is irrelevant as the charger should cut at the desired state of charge. Most chargers cut at 100%. The Luna advanced and mini can cut at a lower SOC which yes, would be safer for cycle life. If you are using a charger that cannot stop at a lower state of charge it will not get as many cycles out of it. You can reference the specs sheets for each cell provided by the manufacturer to see how many cycles you would expect charging to 100%.

The key here is that it is not about letting it go all night, it is about whether the charger is smart enough not to charge the battery to 100% unless you wanted to (for example if you were right about to leave for a long ride and wanted to maximize range)